Tapered needle



United States Patent 3,386,438 TAPERED NEEDLE Peter A. Stevens, Middlebury, Conn., assignor to Roehr Products Company, Inc., a corporation of Delaware Filed July 7, 1965, Ser. No. 470,113 Claims. (Cl. 128-221) ABSTRACT OF THE DISCLOSURE A cannula for cutaneous penetration having a sharp tip for cutting the skin. The shank of the cannula rearwardly of the tip decreases in diameter to provide a minimal friction penetration thereof through the skin by virtue of the enlarged cut made in the skin by the tip which has the maximum cross-sectional area.

Specification This invention relates to cannulae for cutaneous penetration.

The use of cannulae associated with other equipment, such as syringes, to penetrate the skin for administering or withdrawing fluids for medical purposes is well known. Cannulae currently in use have a relatively constant crosssection along substantially their entire length. When such cannulae are inserted through the skin, the edges of the slit caused by the penetration of the point portion resiliently bear against the outer surface of the cannulae. As a result, there is substantial friction between the shank of the cannula and the cutaneous tissue through which the cannula is being inserted. Such friction produces a drag on the cannula as it is being inserted thereby hindering further penetration and causing pain. Various means of lessening such friction to reduce such pain have been employed. Primarily, such means have been limited to the use of various types of lubricants on the shank of the cannula, e.g. silicone lubricants, to reduce such friction. The use of such lubricants, however, introduces the possibility of adverse after effects due to reactions of the tissue to the lubricant. It has been found, for example, that silicones cause the tissues to exude blood for a protracted period of time. One attempt to overcome this serious and vexatious problem has been to provide cannulae having generally planar, enlarged points projecting substantially outwardly of either side of the shanks thereof. Such large, flat tips provide an excessively wide slit during penetration of cutaneous tissue and do not satisfactorily reduce the frictional drag as the skin is still subjected to stretching in a direction transverse to the fiat plane of the tip. Another problem encountered with the known cannulae is the tendency thereof to core, i.e. have a plug of flesh pass into the lumen, or axial passage, of the cannula and plug the passage. The present invention comprehends an improved cannula construction eliminating each of the above discussed discussed disadvantages of the known cannulae in a novel and simple manner.

It is, therefore, the principal object of the present invention to provide a new and improved cannula wherein friction of insertion is eifectively minimized without resorting to the use of lubricants and the like.

More specifically, it is an object of the invention to provide a new and improved cannula that provides easier penetration of the skin and reduced pain by effectively eliminating drag of the tissue by the cannula.

Another object of the invention is the provision of such a cannula wherein the shank portion of the cannula has a transverse dimension in substantially all directions about the axis thereof smaller than the maximum corresponding transverse dimensions of the point portion "ice thereof whereby after initial penetration of the skin -by the point portion, the cannula may pass freely through the resultant slit.

Yet another object of the invention is the provision of such a cannula wherein the shank tapers rearwardly from the point portion thereof.

Still another object of the invention is the provision of such a cannula wherein the shank includes a portion interposed between the tapered portion and the point portion and having a cross-section substantially equal to the maximum cross-section of the point portion.

A still further object of the invention is the provision of such a cannula wherein the 'rearmost portion of the shank includes a cylindrical section.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompaying drawings wherein:

FIGURE 1 is a side elevation of a needle embodying the invention, having a portion thereof broken away;

FIGURE 2 is a side elevation of another form of needle embodying the invention, having a portion thereof broken away;

FIGURE 3 is a side elevation of still another form of needle embodying the invention, having a portion thereof broken away; and

FIGURE 4 is a vertical section of yet another form of needle embodying the invention.

In the exemplary embodiment of the invention as disclosed in FIGURE 1 of the drawing, a cannula generally designated 10 includes a rearwardly enlarging point portion 11 having its maximum dimension transverse to the longitudinal axis of the cannula 10, taken generally at a radial plane indicated at 12. As shown, the point portion 11 defines a sharp leading tip 13 for cutaneous penetration. While the point portion 11 has been shown as the well known flat type of point, those skilled in the artwil appreciate that any other type of point, such as the well known lancet point, could be used in place thereof.

The cannula 10 further includes a shank 1-4 which tapers frusto-conically rearwardly from the point portion 11. As a result thereof, the maximum dimensions of the shank 14 in all radial directions transverse to the longitudinal axis of the cannula 10 rearwardly of plane 12, such as at the radial plane 15, are less than the corresponding maximum transverse dimensions of the point portion 11. Accordingly, when the cannula It} is inserted through the skin tissue, the edges of the slit formed by the point portion 11 will be determined by the maximum transverse dimensions of the point portion 11 at plane 12. As the cannula is further inserted into the tissue, by virtue of the narrowing taper and decreasing periphery of shank portion 14 the tissue will not be subjected to a dragging action, but rather, substantially all portions of the outer surface of shank 14 will recede somewhat inwardly away from the slit edges thereby minimizing friction therebetween. The tissue will not be stretched by virtue of drag by shank 14 and pain, such as heretofore associated with such cannula insertions, is eifectively minimized.

Cannula 1t) defines an axial lumen, or bore, 16. Lumen 16 may have its surface parallel to the outer surface of shank 14 and point portion 11, as shown in FIGURE 1, or, if desired, may be cylindrical as illustrated in the modified needle 20 of FIGURE 2. As shown in FIGURE 1, cannula 10 is provided with a suitable hub 17 for facilitated connection to associated apparatus (not shown) with which it is to be used. Hub 17 includes a central flow passage 18.

Referring now to FIGURE 2, a second exemplary form of a cannula 116 is shown which is generally similar to the cannula 10 shown in FIGURE 1. The structural elements of cannula similar to those of cannula 10 are given similar numerals except one hundred higher. As discussed above, lumen 116, rather than having its surface parallel to the outer surface of shank 114, as is the case with lumen 16 of cannula 10, is cylindrical. The rearmost end 119 of the cannula 111} includes an externally cylindrical portion to facilitate the securing of a suitable hub 117. Cannula 11th functions in substantially the same manner as cannula 10.

A third exemplary form of a cannula 210 embodying the invention is shown in FIGURE 3. The structural elements of cannula 210 similar to those of cannula 10' are given similar numerals except two hundred higher. Cannula 210 differs from cannula It} in that the shank 2145 of cannula 210 includes a short externally cylindrical section 22 0 having a diameter substantially equal to the maximum diameter of point portion 211 (as at plane 212.). Section 220 is disposed between point portion 211 and a rearwardly tapering portion 214. Section 220 of the shank 214- serves to insure that the slit formed in the skin is actually enlarged to substantially the maximum cross section of the point portion, rather than merely stretched to pass the point 211 to thereafter resiliently contract to have frictional engagement with the shank 214 as insertion is continued.

A fourth exemplary form of a cannula 316 embodying the invention is shown in FIGURE 4. The structural elements of cannula 310 similar to those of cannula 10 are given similar numerals except three hundred higher, Cannula 31 0 includes a forward cylindrical section 320 having a diameter substantially equal to the maximum diameter of point portion 311 (as at plane 212). Cannula 318 is also provided with a rear, small diameter, cylindrical section 321 to which hub 317 is secured. Hub 317 includes a central flow passage 318.

The cannulae 10, 110, 21% and 319 may be formed as desired; e.g., they may be formed from suitable blanks comprised of tapered tubes. The blanks may be formed from cylindrical tubes suitably ground to provide the disclosed taper.

Thus, the invention comprehends a new and improved cannula permitting facilitated, friction-free cutaneous penetration without the use of inimical lubricants. As a result, pain is effectively minimized. The gradual decrease of the cross section of the shank over its effective tissue penetration length permits easy movement through the relaxed skin during subsequent withdrawal.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many'rnodifications. Changes, therefore, in the construction and arrangement may be made without depart- 4 7 ing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A cannula for cutaneous penetration comprising a tubular element having a shank and a point portion, said point portion comprising a rearwardly enlarging, sharp leading tip for effecting cutaneous cutting, the maximum transverse dimensions of said point portion being greater in substantially all radial directions than the radially corresponding transverse dimensions of said shank over substantially the entire length of the latter with no transverse dimension of the shank being greater than the maximum transverse dimension of the cutting tip, whereby cutaneous friction during subsequent penetration by said shank is effectively minimized.

2. The cannula of claim 1 wherein said shank includes a portion having a periphery of gradually decreasing length extending from said cutting tip.

3. The cannula of claim 1 wherein said shank includes a rearwardly tapering portion extending from said point portion.

4. The cannula of claim 1 wherein said shank tapers substantially constantly rearwardly from said cutting tip along its entire length.

5. The cannula of claim 1 wherein said shank comprises first and second portions, said first portion tapering rearwardly from said cutting tip to said second portion, said second portion being cylindrical.

6. The cannula of claim 3 wherein said rearwardly tapering portion comprises the major portion of said shank, said shank further including a cylindrical portion interposed between said tapering portion and said cutting tip.

7. The cannula of claim 6 wherein said shank includes a second cylindrical portion at the rear end thereof.

8. The cannula of claim 1 wherein said shank is frustoconical.

9. The cannula of claim 1 wherein each of said shank and cutting tip is frusto-conical.

10. The cannula of claim 1 wherein said cutting tip is frusto-conical.

References Cited UNITED STATES PATENTS 2,187,259 1/1940 Barnhart 128-221 3,007,472 11/ 1961 Nitz 12 8-221 3,238,942 3/1966 Lincolf 128339 RICHARD A. GAUDET, Primary Examiner. D. L. BAKER, Assistant Examiner. 

